Spark plug safety shield

ABSTRACT

A flame and explosion preventive safety shield for detachable securement to the head block of an internal combustion engine in surrounding and encasing relation to each spark plug to provide a structural flame barrier between the spark plug and its high tension lead and the ambient atmosphere surrounding the engine. The safety shield incorporates a spark coil and a secondary lead for supplying high voltage current to the spark plug and one or more fine mesh wire screens arranged to form a heat sink-type flame barrier around the spark plug and the high voltage secondary lead of the spark coil to thereby isolate the spark plug and its high voltage lead from a potentially combustible atmosphere surrounding the engine.

France 169/2 A O United States Patent 1191 Brenholts Feb. 19, 1974 SPARK PLUG SAFETY SHIELD Prima ExaminerLaurence M Goodrid e 1r h 11 T g [75] Inventor A red R Bren o Houston ex Attorney, Agent, or FirmWilliam S. Rambo [73] Assignee: Stitt Spark Plug Company, Conroe,

Tex.

[22] Filed: Mar. 30, 1972 [57] ABSTRACT [21] Appl' 239554 A flame and explosion preventive safety shield for detachable securement to the head block of an internal [52] US. Cl 123/148 A, 123/198 1), 123/169 PH combustion engine in surrounding and encasing rela- [51] Int. Cl. F02p 11/00 tion to each spark p g to p de a structural flame [58] Field of Search ..123/148 A, 148 S, 198 D, barrier between the spark plug and its high tension 123/1 9 R, 1 9 P 193 1 9/2 A lead and the ambient atmosphere surrounding the eni uwflfimm gine. The safety shield incorporates a spark coil and a [56] Ref r Cit d secondary lead for supplying high voltage current to UNITED STATES PATENTS the spark plug and one or more fine mesh wire screens arranged to form a heat sink-type flame barrier $25 1? around the spark plug and the high voltage secondary 2423728 7/1947 Ray "123/198 DC lead of the spark coil to thereby isolate the spark plug 2I231Is45 2 1941 Curran 123/198 DC and its high voltage lead from a Potentially Combusti- 1,956,805 5 1934 Meyer 123/169 PH ble atmosphere Surrounding the'eflgine- FOREIGN PATENTS OR APPLICATIONS 5 Claims, 3 Drawing Figures 707,421 4/1931 PATENTEBFEB I 9 I974 TO PRIMARY IGNITION CIRCUIT SPARK PLUG SAFETY SHIELD BACKGROUND OF THE INVENTION The present invention relates generally to spark plugfired internal combustion engines, and more specifically to a spark plug safety shield for isolating the spark plug and its high voltage lead from a potentially combustible ambient atmosphere surrounding the engine.

In the past, many disasterous fires and/or explosions have occurred as a result of flames or electrical sparks or arcs emanating from a faulty or improperly installed spark plug and/or its high tension lead wires. The danget of a fire or explosion caused by the ignition of a combustible outside atmosphere by a faulty, damaged, or improperly installed spark plug, or by a loose or worn high tension lead, is particularly prevalent in stationary, industrial-type internal combustion engine installations in which the engine is equipped with a dual ignition system which utilizes two spark plugs to tire each cylinder of the engine. For example, if one of the spark plugs of the engine is loosely installed in the spark plug socket, or otherwise becomes loosened or damaged during engine operation, the continued ignition of the fuel mixture within the associated cylinder of the engine oftentimes results in open flame propogation around or through the loosened or damaged spark plug, or even a complete blowout of the spark plug or its insulator. Also, badly worn or otherwise faulty spark plugs and the high voltage lead wires therefor oftentimes cause external electrical arcing sufficient to ignite a combustible atmosphere around the engine with disasterous results.

While previous attempts have been made to reduce the fire and explosion hazards attendant to spark plugfired engines through the use of so-called shielded ignition systems, by and large such shielded ignition systems are subject to numerous objections. Shielded ignition systems rob the high tension leads of voltage due to the inherent capacitance of these systems, and may even increase fire hazards by external arcing between the inner high tension lead wire and the external, braided shielding cable in the event the insulation of the shielded" cable should break down from prolonged usage, or otherwise be broken or damaged.

SUMMARY AND OBJECTS OF THE INVENTION The present invention comprises a safety shield for attachment to the head block of an internal combustion engine adjacent each spark plug for the purpose of providing a structural, foraminous flame barrier around the spark plug and its high voltage lead to thereby minimize, if not prevent, the possibility of explosion or fire from a flame or an electrical are occurring in the immediate area of the spark plug. The present safety shield includes a rigid supporting frame or bracket for detachable connection with the engine head block; at least one, and preferably two, fine mesh wire screen (heat sink) carried by the supporting frame in encasing relation to the spark plug and its associated socket; and a spark coil carried by the supporting frame and having a low voltage, primary lead wire extending exteriorly of the wire screen and a high voltage, secondary lead extending interiorly of the screen for direct electrical contact with the electrode terminal of the spark plug.

The principal object of this invention is to provide a structurally simple, yet mechanically efficient, device for preventing fires or explosions which might otherwise result from the occurrence of an open, external flame or electrical arc at or around the spark plug and 57 voltage lead of an internal combustion engine.

Another object is to provide a spark plug safety shield which includes a unitized spark coil and high tension lead for connection with the electrode terminal of the spark plug, and wherein the: safety shield is arranged to provide a protective flame and spark barrier around both the spark plug and the high tension lead therefor.

A further object of the invention is to provide a spark plug safety shield which is readily attachable to and detachable from conventional spark plug-fired internal combustion engines without requiring extensive modification of the engine, and which, when attached to the engine, affords a double check on the proper installation and seating of an associated spark plug.

Yet another object is to provide a spark plug safety shield of the aforementioned character which incorporates a normally closed thermal switch operable automatically in response to an overheated condition in the area of the spark plug to open the primary ignition circuit of the associated engine and thereby stop the engine until the cause for the overheated condition is detected and remedied.

These and other objects and advantages of the present invention will become more readily apparent by reference to the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view taken through the head block of an internal combustion engine in the area of one of the spark plugs of the engine and showing the present safety shield in its operatively installed position;

FIG. 2 is a fragmentary top plan view of the safety shield installed on the engine head block; and

FIG. 3 is an enlarged, fragmentary vertical sectional view illustrating the connection between the high voltage lead of thespark coil and the electrode terminal of the spark plug.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION Referring now to the drawings, it will be seen that the present safety shield takes the form ofa generally hemispherical, dome-shaped, unitary assembly which comprises a rigid supporting frame made up ofa central, cylindrical, container-like housing 10 and a plurality of relatively spaced, outwardly and downwardly extending bracket arms 11. The central housing 10 is open at its lower end and is closed at its upper end by an integral top wall 12. Each of the bracket arms 11 are formed with upper end tabs or bosses 13 which are preferably welded or otherwise rigidly secured to the outer side wall of the central housing 10. The arms 11 terminate at the lower ends thereof in radially outwardly extending, relatively flat attachment flanges 14 formed with side-opening, bolt-receiving slots 15.

The safety shield further comprises at least one, and preferably two, relatively fine mesh, metal wire screens 16 and 17 of a type similar to those used as heat sink screens in the old acetylene gas-fired Miner's lamps or torches. Both of the screens 16 and 17 are of generally inverted bowl-shaped configuration; having a curvature conforming closely to the curvature of the main body portion of the bracket arms 11. Each of the screens 16 and 17 is formed with a central opening approximating the outer diameter of the housing 10, and each screen is welded, or otherwise securely fastened, to the lower end portion of the housing 10. Additionally, the screens are welded, or otherwise securely fastened at their lower edges to each of the bracket arms 11. Preferably, the screens 16 and 17 are disposed in relatively spaced apart, concentric relation to one another, so as to provide an air space therebetween, and the innermost screen 16 is preferably formed with a rolled or beaded lower circumferential edge 18 for snug fitting engagement with the outer surface of the engine head block Press-fitted, or otherwise secured, in the housing is the outer casing of a high voltage spark coil 20. The spark coil 20 is provided with the usual low voltage, primary lead wires 21 through which relatively low voltage D.C. operating current is intermittently supplied to the primary winding (not shown) of the spark coil 20 by the low voltage distributor (not shown) of the engine. The primary lead wires 21, which are themselves insulated, extend outwardly through a pair of openings 22 formed in the end wall of the housing 10. Each of the openings 22 are provided with dielectric bushings or grommets 23 to additionally electrically insulate the lead wires 21 from the metal housing 10. The outer metal casing of the spark coil 20 acts as a ground terminal for the secondary, high voltage winding (not shown) of the spark coil 20. The outer casing of the spark coil is, in turn, adapted to be grounded to the engine head block 19 by means of the metal housing 10 and the metal bracket arms 11 and/or screens 16 and 17, when the safety shield is connected to the head block as shown in FIGS. 1 & 2.

Extending outwardly from the lower or inner end of the spark coil 20, and electrically insulated from the outer casing thereof, is a single high voltage, secondary lead 24. The lead 24 preferably comprises a rigid, solid rod of electrically conductive metal which is formed at its outer end with a cylindrical socket 25 arranged to telescope over the outer end portion of the electrode terminal 26 of a spark plug 27 which is threaded and securely fastened in the cooperatively threaded spark plug socket 28 of the engine head block 19. As shown in H0. 3, the socket 25 of the rod-like lead 24 preferably contains a spring-pressed, plunger-type contact block 29 to insure a tight-fitting electrical connection between the lead 24 and the electrode terminal 26 of the spark plug 27, while at the same time compensating for the normal thermal expansion and contraction of the lead 24 in response to variations of operating temperatures.

As shown diagrammatically in FIG. 1, the safety shield also preferably includes a thermocouple or equivalent temperature-sensing device 30 which is carried in association with the supporting frame of the safety shield. Connected with the temperature sensing device 30 is a normally closed switch 8 having remotely extending lead wires 31 for electrical series connection with the primary or main low voltage ignition circuit (not shown) for the engine. The switch S, when so connected, is operable automatically in response to an abnormal high temperature or overheating condition in and around the safety shield (such as might be occasioned by a loose or blown spark plug, or a short circuit in or around the high voltage lead 24) to open and interrupt the main ignition circuit for the engine and thereby stop the engine until the cause for the overheating condition may be detected and remedied.

In operation, the safety shield is installed by placing it over and around the spark plug 27 with the outer socketed end of the secondary lead 24 telescoping the electrode terminal 26 of the spark plug. The connector flanges 14 of the bracket arms 11 are then securely fastened to the head block 19 ofthe engine by the bolts 32. Should it happen that the spark plug 27 has been installed loosely in its socket 28, through inadvertence, this condition will normally be detected when the installer or mechanic attempts to connect the secondary lead rod 24 of the safety shield with the abnormally elevated electrode terminal of the spark plug, and this undesired, hazardous condition may then be corrected before the engine is started. After bolting the safety shield in place, the necessary electrical connections are made between the low voltage leads 21 of the spark coil 20 and the engine distributor, and between the thermally responsive switch S and the primary ignition circuit of the engine. The engine is then in condition for operation.

In the event the spark plug becomes sufficiently loose in its socket, or otherwise becomes damaged, broken or blown during engine operation to the extent that an open flame is projected outwardly from the spark plug socket, the fine mesh wire screens 16 and 17 will function as heat sinks, as well as a structural barrier, to confine the flame within the safety shield and prevent it from igniting a potentially combustible or explosive atmosphere in the surrounding engine room or compartment. By the same token, the safety shield guards against the ignition of a potentially explosive, ambient atmosphere in the event of electrical arcing or flash over" at or around the spark plug and the high voltage lead of the spark coil. The safety shield also functions as a structural barrier in the event of a spark plug blowout and normally will prevent a blown spark plug or parts thereof from being forcibly projected from the engine with attendant hazards. In this regard, the archshaped bracket arms 11 of the supporting frame in combination with the wire mesh screens 16 and 17 provide a high strength, dome-like encasement over and around the spark plug, and the solid, secondary lead rod 24, which directly engages the electrode terminal of the spark plug, tends to hold the spark plug against undesired, accidental displacement from its socket. The wire mesh screens 16 and 17 are preferably formed of stainless steel, or nickel-plated copper wire, so as to provide a comparatively strong structural barrier between the rigid bracket arms ll of the frame. At the same time, the perforate or foraminous nature of the screens 16 and 17 provides ample ventilation around the plug and provides for the escape of ozone gas which might be generated by electromagnetic forces around the spark plug and the spark coil 20.

In view of the foregoing, it will be seen that the present invention provides an improved spark plug safety shield which may be readily and easily installed on an engine to provide an efficient flame and spark barrier around the spark plug and the associated high voltage spark coil and its secondary lead. The present safety shields also afford a means for interrupting the operation of the engine in the event of overheating resulting from faulty, damaged, or worn spark plugs and/or their associated high voltage leads.

While a presently preferred embodiment of the invention has been illustrated and described in detail, it will be understood that various modifications in details of construction and design may be made without departing from the spirit of the invention or the scope of the following claims.

I claim:

1. In combination with an internal combustion engine having a head block, a spark plug removably carried in said block and an ignition circuit for controlling operation of said engine; a fire and explosion-preventive safety shield comprising:

a. a rigid frame detachably connected with the head block of said engine adjacent said apark plug;

b. a spark coil carried by said frame in spaced relation to said spark plug and having a high voltage lead extending to and detachably engaging the electrode terminal of said spark plug; and

c. a relatively fine mesh wire screen carried by said frame in relatively spaced, but encasing, relation to said spark plug and the high voltage lead of said spark coil and defining a substantially uninterrupted flame and spark-confining, heat sink barrier around said spark plug and the high voltage lead of said spark coil.

2. The combination defined in claim 1, wherein said frame, said screen and said spark coil comprise a unitary structure for quick detachment from the head block of said engine, and the high voltage lead of said coil comprises a substantially rigid rod extending from said coil interiorly of said screen for electrical engagement with the electrode terminal of said spark plug.

3. The combination defined in claim 1, wherein said frame, said screen and said spark coil comprise a unitary, dome-like structure disposed in relatively spaced, encasing relation to said spark plug.

4. The combination defined in claim ll, including a second relatively fine mesh wire screen carried by said frame in relatively spaced apart relation to said firstnamed screen.

5. The combination defined in claim 1, including a normally closed thermally-responsive switch means carried by said safety shield and having a remotely extending conductor for electrical connection with the ignition circuit of said engine, said. switch means being operable in response to a given high temperature at said safety shield to interrupt the ignition circuit of said engine. 

1. In combination with an internal combustion engine having a head block, a spark plug removably carried in said block and an ignition circuit for controlling operation of said engine; a fire and explosion-preventive safety shield comprising: a. a rigid frame detachably connected with the head block of said engine adjacent said spark plug; b. a spark coil carried by said frame in spaced relation to said spark plug and having a high voltage lead extending to and detachably engaging the electrode terminal of said spark plug; and c. a relatively fine mesh wire screen carried by said frame in relatively spaced, but encasing, relation to said spArk plug and the high voltage lead of said spark coil and defining a substantially uninterrupted flame and spark-confining, heat sink barrier around said spark plug and the high voltage lead of said spark coil.
 2. The combination defined in claim 1, wherein said frame, said screen and said spark coil comprise a unitary structure for quick detachment from the head block of said engine, and the high voltage lead of said coil comprises a substantially rigid rod extending from said coil interiorly of said screen for electrical engagement with the electrode terminal of said spark plug.
 3. The combination defined in claim 1, wherein said frame, said screen and said spark coil comprise a unitary, dome-like structure disposed in relatively spaced, encasing relation to said spark plug.
 4. The combination defined in claim 1, including a second relatively fine mesh wire screen carried by said frame in relatively spaced apart relation to said first-named screen.
 5. The combination defined in claim 1, including a normally closed thermally-responsive switch means carried by said safety shield and having a remotely extending conductor for electrical connection with the ignition circuit of said engine, said switch means being operable in response to a given high temperature at said safety shield to interrupt the ignition circuit of said engine. 